Silicon carbide (SiC) has excellent physical properties to exhibit a band gap about three times wider, dielectric breakdown field strength about ten times stronger and thermal conductivity about three times greater, than those of silicon (Si). Therefore, the applications of SiC to a power device, a high frequency device, a high-temperature operation device or the like have been expected.
For the promotion of practical application of SiC devices, it is essential to establish a high-quality crystal growth technique and a high-quality epitaxial growth technique.
SiC has a number of polytypes. The polytype mainly used for producing a practical SiC device is 4H—SiC. A substrate of a SiC device is prepared by forming a SiC epitaxial film to serve as an active region of the SiC device through a chemical vapor deposition (CVD) method, on a SiC single crystal substrate processed from a bulk crystal produced by the sublimation method or the like. Polytypes different from the polytype used in the substrate are easily introduced into the epitaxial film. For example, in the case of using the 4H—SiC polytype in the substrate, polytypes of 3C—SiC and 6H—SiC are introduced. In order to suppress the introduction of these polytypes, epitaxial growth is generally performed by slightly tilting the crystal face of the SiC single crystal substrate to allow step-flow growth (growth in the lateral direction from the atomic steps).
In the crystals of SiC, for example, as described in Patent Document 1, various types of defects are present, including point defects such as carbon vacancies and mixed impurity atoms, linear defects such as threading screw dislocations, threading edge dislocations and basal plane dislocations, and planar defects such as stacking faults. There are the so-called triangular defects among these defects. A triangular defect is a defect that is formed with a characteristic surface morphology on the surface of an epitaxial layer on a vicinal SiC single crystal substrate having an off angle.
It has been required to reduce these defects since they adversely affect the properties, yield and reliability and the like of SiC devices.
In recent years, in order to increase the effective area of the wafer, reduction of the edge exclusion (ineffective region in the periphery of the semiconductor wafer, usually represented by the distance from the edge), together with an increase in the size of the wafer has been desired.
If it is possible to reduce the edge exclusion, the effective area ratio for producing chips increases, and the yield of the semiconductor chip is improved. For this reason, it has been required to make the width of the edge exclusion even smaller.